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ACEEE Int. J. on Control System and Instrumentation, Vol. 02, No. 02, June 201 1 



A New Soft-Switched Resonant DC-DC Converter 

Rogayeh Pourabbasali 1 , Samira Freghi 2 , Reza Pourabbasali 3 and Majid Pakdel 4 
Islamic Azad University, Miyaneh Branch/ Iran 12,4 

Ro. Pourabbasali@yahoo.com 

Islamic Azad University, Shabestar Branch/ Iran 3 

Fareghi_s@yahoo.com ,Reza9099@ yahoo.com ,majidpakdel@ yahoo.com 



Abstract- This paper presents a new soft-switched resonant dc- 
dc converter using a passive snubber circuit. The proposed 
converter uses a new zero voltage and zero current switching 
(ZVZCS) strategies to get ZVZCS function. Besides operating 
at constant frequency, all semiconductor devices operate at 
soft-switching without additional voltage and current stresses. 
In order to validate the proposed converter, computer 
simulations and experimental results were conducted. The 
paper indicates the effective converter operation region of the 
soft-switching action and its efficiency improvement results 
on the basis of experimental evaluations using laboratory 
prototype. 

Index Terms- ZVZCS, resonant, converter, semiconductor, 
current switching, snubber 

I. Introduction 

There has been an increasing interest in the soft-switching 
power conversion technologies in order to overcome the 
limitations of the hard-switching technologies [l]-[7]. Soft- 
switching (SS) converters had many advantages over hard- 
switching (HS) converters. For example, SS converters lower 
switching losses, reduce voltage/current stress, reduce EMI, 
and allow a greater high switching frequency in high power 
applications [1]. Despite the advantages of SS converters, 
its applications have been so far limited due to complexity in 
the design of SS circuits, and difficult in control realization. 
There has been a growing demand for a simple design that 
provides reliable control in a wide-range of operational 
condition. Several SS techniques have been developed such 
as the auxiliary resonant snubber inverter (RSI) [1], the 
auxiliary resonant commutated pole inverter (ARCP) [3], [6], 
the inductor coupled zero-voltage transition inverter (ZVT) 
[4]-[5], and the resonant dc link inverter (RDCL) [2], [7], [8]. 
The RSI is suitable for single or three-phase inverters with 
multiple branches of auxiliary circuits but needs modification 
of space vector modulation to ensure zero voltage switching. 
The ARCP requires large split capacitors to achieve a zero- 
voltage switching. The ZVT requires bulky coupled inductors 
to reset the resonant current. The RDCL needs a device 
voltage rating higher than that which has been used in other 
converters. To realize high conversion efficiency, a soft 
switching circuit is useful and effective technologies. And 
many soft-switching circuits applied to dc-dc converter have 
been proposed [9]-[22]. Among of these technologies, the 
soft-switching topologies using an auxiliary active switch 
method have disadvantages, such as low reliability and 
complexity of both the power circuit and control circuit 
compared to the passive soft-switching ones. The passive 
Snubber circuit has the simple circuit configuration and wide 

©2011 ACEEE 
DOr.01.LTCSI.02.02.5 



operation region of the soft-switching action [12], [13]. This 
paper presents the snubber circuit which consists of the 
passive components applied to the dc-dc converter. Due to 
its simple circuit configuration, this proposed converter is 
able to be controlled by a single PWM signal, establishing 
high reliable circuit. In order to validate the proposed 
converter, computer simulations and experimental results were 
conducted. In the simulation and experimental results, the 
purpose of the comparison between soft-switching and hard- 
switching was to investigate the following characteristics: 
the voltage spike, EMI noise, turn-off dv/dt, heat sink 
temperature, power loss and control flexibility. With the merits 
of simplicity and flexibility, the proposed dc-dc converter 
shows excellent performance and potential for various 
industry applications including switched reluctance motor 
(SRM) drives, high-frequency-high-voltage choppers, 
magnet drivers, and magnetic resonance imaging (MRI) 
system applications. 

II. Proposed Converter Topology and its Operations 

A. Operation Principles 

The conventional dc-dc converter circuit is shown in Fig. 
1 . Fig. 2 illustrates the circuit configuration of the proposed 
soft-switched resonant dc-dc converter which uses the 
passive snubber circuit , and which can be operated under 
the principle of low dv/dt and di/dt turnoff and turn on 
(ZVZCS) and simple PWM action. The main power converter 
circuit consists of one active switch (Q) and the auxiliary 
passive snubber circuit. 




Fig. 1. Conventional dc-dc converter. 




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Fig. 2. Proposed soft-switched resonant dc-dc converter. 



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ACEEE Int. J. on Control System and Instrumentation, Vol. 02, No. 02, June 201 1 



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La 






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Mod= 1 




Mode 3 




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Mods 4 




Vout 



Mode 5 
Fig. 3. Operation modes. 

A. Circuit Analysis 

Fig. 3 indicates operation mode transition diagram of the 
proposed soft-switched resonant dc-dc converter. Operation 

©2011 ACEEE 
DOI:01.LTCSI.02.02.5 



of the proposed resonant dc-dc converter circuit is as follows: 

Mode 1 At mode 1, the active switch Q is turned on and a 

voltage 

nVin is reflected across the secondary winding of the main 

inductor. As a result, resonance based on Lr and Cr starts 

partially. The snubber capacitor voltage is discharged toward 

to low level. 

Mode 2 When the snubber capacitor voltage is fully 
discharged to zero, at this time, the additional operation mode 
of mode 2 is started, and the Cr current decreases linearly to 
release the resonant inductor energy. When the Cr current 
becomes zero, mode 3 starts. 

Mode 3 The main inductor energy is stored from the input 
side in this mode. When the active switch is turned off by the 
controller gate off signal of duty ratio (+), mode 4 starts 

Mode 4 At this mode, the turn-off voltage applied to the 
active switch is suppressed by the snubber capacitor, and 
then the turn-off loss of the active switch becomes small. 
When the capacitor voltage reaches to Vin +Vout , mode 5 
starts. 

Mode 5 The energy stored in the main inductor is released to 
the output side in this mode. 

Since deep discharge of the snubber capacitor can be 
obtained at the condition of small value of Vout /Vin , the 
large reduction of the turn-off loss of the active switch can 
be achieved. This means that the higher input voltage at the 
output constant voltage control condition grants the larger 
effectiveness of the efficiency improvement. 

III. Simulation Results 

The proposed two quadrant soft switched converter in 
the PSIM software environment is shown in Fig. 4. The 
following circuit parameters have been used in simulations: 

1) A MOSFET module at 400V - 10A was used; 

2) The resonant capacitor Cr used was 120 nF- 50V 
polypropylene capacitor; 

3) The resonant inductor Lr used was 47 /.iH ; 

4) The snubber inductor Ls used was 10 /uH ; 

5) The snubber capacitor Cs used was InF; 

6) The input and output capacitors (Cin and Cout) used 
were 410/uF ; 

7) The diodes D and Dr used were 1 N4500; 

8) The resistance 1&! is used as a load. 

The waveforms of vds and ids of the switch Q is shown in 
Fig. 5. The output dc voltage (Vout) is shown in Fig. 6. The 
simulation results show that the proposed soft switched 
resonant dc-dc converter has the proper response. 



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ACEEE Int. J. on Control System and Instrumentation, Vol. 02, No. 02, June 201 1 



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Fig. 4. Proposed soft switched resonant dc-dc converter in PSIM 
software 






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Fig. 5. Vds and Ids wav 


sforms of the switch. 








































Fig. 6. Output dc voltage (Vout). 

simulation results show that the proposed soft switched 
resonant dc-dc converter has the proper response. 

IV. Experimental Results 

A Prototype of the proposed converter, as shown in Fig. 7 
has been built in the laboratory. The newly proposed 
converter operates with an input voltage Vs = 3.67V, output 
voltage Vo = IV, load current of 0.6A and a switching 
frequency of 50 kHz. The V m and V GS waveforms of MOSFET 
switch in a time period of one switching cycle are shown in 
Fig. 8 and Fig. 9 respectively. The voltage across resonant 
capacitor 120nF is shown in Fig. 10. The clock signal in a time 
period of one switching cycle is shown in Fig. 1 1 . The output 
DC voltage is shown in Fig. 12. 




Fig. 7. Prototype of the proposed converter. 




Fig. 8. Drain-source (V DS ) signal: 
Volt/Div = 0.5 v, Time/Div= 10 JUS , V m =3.66 v, I =0.6A 




Fig. 9. Gate signal: 
Volt/Div = 5v, Time/Div= 10 JUS , V in =3.67 v, I„=0.6A 



©2011 ACEEE 
DOr.01.LTCSI.02.02.5 



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ACEEE Int. J. on Control System and Instrumentation, Vol. 02, No. 02, June 201 1 




Fig. 10. Voltage across resonant capacitor 120 nF: 
Volt/Div = 50 mv, Time/Div= 10 JUS , V in =3.62 v, I m =0.6A 




Fig. 1 1 . The clock signal: 
Volt/Div = 1 v, Time/Div= 10 /US , V. =3.67 v, I. =0.6A 




Fig. 12. The output DC voltage: 
Volt/Div = 1 v, Time/Div= 0.5 ms, V jn =3.67 v, L 



V. Conclusion 



=0.6A 



In this section, a new soft-switching converter topology 
with a simple resonant snubber circuit was proposed and 
was verified fully for working conditions with a load. In order 
to verify performance of the proposed converter, circuit 

©2011 ACEEE 
DOi:01.LTCSI.02.02.5 



simulations using PSIM software and experimental results 
were given. With the merits of simplicity and flexibility, the 
proposed soft switched dc-dc converter shows excellent 
performance and potential for various industry applications 
including switched reluctance motor (SRM) drives, high-fre- 
quency-high-voltage choppers, magnet drivers, and magnetic 
resonance imaging (MRI) system applications. The opera- 
tion principle of the proposed circuit, its design consider- 
ation and efficiency characteristic are described on the basis 
of theoretical and experimental point of view. It is verified 
that the efficiency of the proposed new soft-switching con- 
verter increases when the passive snubber circuit is imple- 
mented compared to the hard-switching operation. 

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